James 5:20 Context

17Elias was a man subject to like passions as we are, and he prayed earnestly that it might not rain: and it rained not on the earth by the space of three years and six months. 18And he prayed again, and the heaven gave rain, and the earth brought forth her fruit. 19Brethren, if any of you do err from the truth, and one convert him; 20Let him know, that he which converteth the sinner from the error of his way shall save a soul from death, and shall hide a multitude of sins.

Bible commentary

Wesley's Notes for James 5:20

5:20 He shall save a soul - Of how much more value than the body! #Jas 5:14|. And hide a multitude of sins - Which shall no more, how many soever they are, be remembered to his condemnation.

People's Bible Notes for James 5:20

Jas 5:20 Let him know. As an inducement to engage in this work of love let him know how great a work has been done. Save a soul from death. Not physical but eternal death. Hide a multitude of sins. The sins of those forgiven are said to be covered or hidden. This passage means that all the sins of the restored sinner, though many, shall be blotted out. See Ps 32:1.

Discussion for James 5

Henrietta; Yes! The Lord Jesus Christ has been given all authority in heaven and on earth; and He has charged us in His name, to proclaim the Glad Tidings to every creature; teaching all men everywhere to keep all His words, everything that He has commanded us; thus also warning the rich that they not foolishly trust in their good things in life, and miss the truth and the word of their salvation.

I see 2 messages: one to the corrupted rich and one to the brethren. The rich will be judged for their fraudulent activities. The brethren are warned to stay pure in heart/ no grudges and to have patience. They are also encouraged to pray earnestly and to pray for the sick to be healed.
Sin and sickness are linked, but both can be remedied by the blood through prayer.